1. Field of the Invention
The present invention relates generally to systems and methods for heat exchange with a patient's airways and lungs for selective modification and control of a patient's body temperature. More particularly, it relates to a system and a method for controlling a patient's core body temperature by introducing frozen particles into the patient's respiratory system while monitoring exhalation temperature.
Normal functioning of the human animal requires a body temperature of approximately 37 degrees Celsius (98.6 degrees Fahrenheit). The body can self-compensate for small upward or downward variations in temperature through the activation of a built-in thermoregulatory system, controlled by temperature sensors in the skin. The response to an upward variation in body temperature is the initiation of perspiration, which moves moisture from body tissues to the body surface. When the moisture reaches the surface it evaporates, carrying with it a quantity of heat. The response to a downward variation in body temperature is shivering, which is the body's attempt to generate heat. Shivering is an involuntary contraction and expansion of muscle tissue occurring on a large scale. This muscle action creates heat through friction.
Hypothermia is defined as a core temperature of less than 35° C. and is considered a clinical state of subnormal temperature when the body is unable to generate sufficient heat to effectively maintain functions. Many variables contribute to the development of hypothermia. Age, health, nutrition, body size, exhaustion, exposure, duration of exposure, wind, temperature, wetness, medication and intoxicants may decrease heat production, increase heat loss, or interfere with thermostability. The healthy individual's compensatory responses to heat loss via conduction, convection, radiation, evaporation and respiration may be overwhelmed by exposure. Medications may interfere with thermoregulation. Acute or chronic central nervous system processes may decrease the effectiveness of thermoregulation.
Recent medical reports have described the use of controlled hypothermia as a means to reduce oxygen consumption of tissue, such as the heart muscle and the brain during decreased perfusion that occurs as a result of myocardial infarction and ischemic stroke (respectively), which leads to reduced damage and decrease of the infarcted area. Medical reports have also described the prophylactic use of controlled hypothermia during cardiac surgery or interventional cardiology procedures for reducing damage from ischemia and/or embolization in the heart and brain during and after the procedure.
U.S. Pat. Nos. 8,100,123; 8,281,786; 8,402,968; and U.S. Patent Publ. No. 2013/0085554, all commonly assigned with the present application and incorporated herein by reference, describe improved systems and methods for inducing hypothermia in patients by introducing ice or other frozen particles into the lungs or other body cavities of the patient. As the frozen particles melt, heat is absorbed by the heat (enthalpy) of melting, and the body of the patient is cooled. While offering considerable advantages of prior systems for inducing hypothermia, the respiratory introduction of ice and other frozen particles can be difficult to control and has the potential to cool a patient beyond any desired therapuetic range.
For those reasons, it would be desirable to provide methods and systems for inducing hypothermia with a reduced risk of overcooling the patient. Such methods and systems should further provide for rapid attainment of a desired core body temperature and subsequent maintenance of the core temperature with minimum deviation. At least some of these objections will be met by the inventions described below.
2. Description of the Background Art
U.S. Pat. Nos. 8,100,123; 8,281,786; 8,402,968; and U.S. Patent Publ. No. 2013/0085554 have been described above. U.S. Patent Publ. 2013/0226077 describes monitoring exhalation temperature in a peritoneal hypothermia system that optionally delivers phase change fluids to the peritoneal cavity.